(a book written by Olivia Judson in 2002. 308pp with copious notes and bibliography.)

Dr. Tatiana is a fictional advice columnist (not to be confused with the author, Olivia Judson) who answers letters from animals that are confused or curious about how sex works in their species. There's the green spoon worm who accidentally inhaled her husband, the sea hares who have wild hermaphroditic orgies and can't understand why everyone else insists on being one sex or the other, the hyena who wants to know why she has a penis, the perch who's disgusted by the slutty females of his species.

The twee anthropomorphism is a cover for discussing evolutionary biology. When a slime mold writes in to ask if it's really true that his species has thirteen different sexes, Dr. Tatiana steps back to explain just what gender is, biologically, and why not all species bother with "male" and "female". In some cases, Dr Tatiana hops from one totally unrelated species to another, explaining how they have sex, before returning to the case at hand. Contrived, yes, but otherwise Judson would have to either cut down on her material, or quit with the cutesy letters. And the letters, while somewhat silly, are actually a very effective way of keeping the book interesting.

Dr Tatiana doesn't so much answer questions as use them to segue into pet topics. The chapters are laid out to illustrate her favorite points. Among them: females are often promiscuous; males are often unnecessary; sex can be a vicious competition between male and female, or between mother and child.

Ever since Darwin wrote about sexual selection, biologists assumed that females were passive participants in sex. Males fought each other for females, or tried to win them over; the female would mate with the winner, bear his children, and that was that. More recently, though, evolutionary biologists have started paying more attention to sex, and the rules turn out to be very different from what Darwin imagined.

The idea that females sleep around at least as much as males do was shocking to many people. (One biologist, Marlene Zuk, commented that her students were more upset by the idea of Mrs Bluebird cheating on Mr Bluebird than by any of the other, categorically nastier, things mentioned in class). I applaud Judson for trying to popularize not only this news, but the more general idea of diversity in the animal kingdom. Being large terrestrial vertebrates, we tend to think of things in a very mammal-centric way. Sex isn't all about males and females and monogamy. Sometimes a male is reduced to a tiny sperm factory and fused to a female's body; sometimes hermaphrodites want to fertilize but not be fertilized, and so there are worms that engage in what can only be called penis jousting. It's a huge weird world, and most of us haven't a clue what's in it.